Charge pumps use a switching process to provide a DC output voltage larger than its DC input voltage. In general, a charge pump will have a capacitor coupled to switches between an input and an output. During one clock half cycle, the charging half cycle, the capacitor couples in parallel to the input so as to charge up to the input voltage. During a second clock half cycle, the transfer half cycle, the charged capacitor couples in series with the input voltage so as to provide an output voltage twice the level of the input voltage. This process is illustrated in FIGS. 1a and 1b. In FIG. 1a, the capacitor 5 is arranged in parallel with the input voltage VIN to illustrate the charging half cycle. In FIG. 1b, the charged capacitor 5 is arranged in series with the input voltage to illustrate the transfer half cycle. As seen in FIG. 1b, the positive terminal of the charged capacitor 5 will thus be 2*VIN with respect to ground.
Charge pumps are used in many contexts. For example, they are used as peripheral circuits on EEPROM, flash EEPROM and other non-volatile memories to generate many of the needed operating voltages, such as programming or erase voltages, from a lower power supply voltage. A number of charge pump designs, such as conventional Dickson-type pumps, are know in the art. But given the common reliance upon charge pumps, there is an on going need for improvements in pump design, particularly with respect to trying to reduce the amount of layout area and the current consumption requirements of pumps.
FIG. 2 is a top-level block diagram of a typical charge pump arrangement. The designs described here differ from the prior art in details of how the pump section 201. As shown in FIG. 2, the pump 201 has as inputs a clock signal and a voltage Vreg and provides an output Vout. The high (Vdd) and low (ground) connections are not explicitly shown. The voltage Vreg is provided by the regulator 203, which has as inputs a reference voltage Vref from an external voltage source and the output voltage Vout. The regulator block 203 regulates the value of Vreg such that the desired value of Vout can be obtained. The pump section 201 will typically have cross-coupled elements, such at described below for the exemplary embodiments. (A charge pump is typically taken to refer to both the pump portion 201 and the regulator 203, when a regulator is included, although in some usages “charge pump” refers to just the pump section 201.)
To provide higher levels, a charge pump will boost the input voltage progressively in a series of stages. In many charge pump applications, such as for a non-volatile memory, several different regulated outputs are often needed concurrently. There is an ongoing need to improve the efficiency of such system by reducing both their power and energy requirements, while retaining accuracy of the output levels.